High intensity discharge (HID) lamps include mercury vapor, metal halide, high and low pressure sodium, and xenon short-arc lamps. HID lamps produce light by generating an electric arc across two spaced-apart electrodes housed inside a sealed quartz or alumina arc tube filed with gas or a mixture of gas and metals. The arc tube is typically filled under pressure with pure xenon, a mixture of xenon-mercury, sodium-neon-argon, sodium-mercury-neon-argon, or some other mixture such as argon, mercury and one or more metal halide salts. A metal halide salt (or metal halide) is a compound of a metal and a halide, such as bromine, chlorine, or iodine. Some of the metals that have been used in metal halide lamps or bulbs include indium, scandium and sodium. Xenon, argon and neon gases are used because they are easily ionized, produce some level of immediate light, and facilitate the striking of the arc across the two electrodes when voltage is first applied to the lamp. The heat generated by the arc then vaporizes the sodium, mercury and/or metal halides, which produce light as the temperature and pressure inside the arc tube increases.
Since HID lamps are negative resistance devices, they require an electrical ballast to provide a positive resistance or reactance that regulates the arc current flow and delivers the proper voltage to the arc. Some HID lamps, called “probe start” lamps, include a third electrode within the arc tube that initiates the arc when the lamp is first lit. A “pulse start” lamp uses a starting circuit referred to as an igniter, in place of the third electrode, that generates a high-voltage pulse to the electrodes to start the arc. Initially, the amount of current required to heat and excite the gases is high. Once the chemistry is at its “steady-state” operating condition, much less power is required, making HID lamps more efficient (producing more light with less energy over a long period of time) than filament based lights.
The majority of light generated by a short gap HID lamp is produced by a small line source of plasma. This relatively small light source enables the output of the HID lamp to be more easily focused into an intense, narrow beam than many other light sources. HID lamps also produce high heat levels close to the lamp. A concave (parabolic or elliptical) shaped reflector, with a through-hole in the bottom through which the HID lamp is inserted, is used to focus the light. A “through-hole” is the hole cut in the bottom of the reflector that allows the HID lamp to protrude into the reflector. Most reflectors are formed from polished aluminum, which is sometimes coated with other reflective materials. The design of the reflector, and in particular the size and shape of the through-hole, has a great effect on the efficiency of the entire electro-optical system. Since heat from the lamp can be transferred to the reflector and through the through-hole and into the ballast assembly, reducing the through-hole and reducing a users need to touch the reflector housing (which may be quite hot), has added importance in HID lamps.
Handheld searchlights and portable lights using HID lamp light production are powerful tools that may be used in both covert and non-convert operations. An ability to manually adjust the focus of such a searchlight during use can be critical. The act of focusing involves adjusting the beam of light produced. Depending upon the focal adjustment made by a user, the beam may be adjusted from a wide beam that will travel a certain distant to a narrow beam that will travel substantially further but obviously not light up as much area. Of course, it may be possible to adjust the light beam continuously, meaning that the searchlight may be adjusted to any point in between the widest beam capable of being produced and the narrowest beam capable of being produced. Focal adjustment is therefore an important feature in a heavy duty or professional handheld/portable searchlight system.
The focus of a searchlight or flashlight is generally adjusted by moving the reflector relative to the HID lamp, along the optical axis. Positioning a HID lamp relatively far into a reflector, meaning that the electric arc is created closer to the searchlight's outer lens and further from the searchlight's ballast, will create a light beam that is wider but travels a shorter distance. On the other hand, positioning a HID lamp shallow into a reflector, meaning that the electric arc is created further from the searchlight's outer lens and closer to the searchlight's ballast, will create a light beam that is narrower but travels a longer distance. Traditionally, the relative position of the HID lamp has been adjusted by moving the reflector along the optical axis while keeping the HID lamp rigidly in place. This is usually accomplished by designing the reflector to attach to the remaining searchlight components by screwing onto threaded stock. Such a design means that if a user either screws the reflector tighter or unscrews the reflector looser, the reflector will move along the optical axis and thus change its position relative to the HID lamp.
There are many drawbacks to relying on screwing the reflector in and out of threaded stock in order to adjust focus. It is possible for a user to accidently unscrew the reflector completely, so that the reflector becomes separated entirely from the remainder of the searchlight. User safety is also at issue because traditional designs ask a user to manually handle and/or rotate the reflector itself in order to screw the reflector in and out of the threaded stock. The reflector housing is subject to intense heat as it reflects the light produced by the HID lamp assembly and can become quite hot during use. Physically handling such a hot reflector can be dangerous. Furthermore, a rotating reflector obviously changes the angular orientation of the reflector relative to the optical axis and relative to the user. If a user intends to switch out the searchlight lens or filter attachment being used and replaces it with another, the user may need to quickly locate the lens/filter attachment points along the rim of the reflector and then detach the current lens/filter. This may prove difficult if the orientation of the attachment points constantly change with every focal adjustment. Additionally, a rotating reflector housing necessarily requires a relatively large through-hole in order to allow the reflector to fully rotate about the HID lamp. This is because a HID lamp's cross-section is not circular —it has an assist, and/or frame, wire that protrudes from the outer shroud of the lamp glass —meaning that a through-hole must be cut to accommodate the assist wire, creating a significantly larger through-hole. A relatively larger through-hole is detrimental to both light beam production (because a significant amount of surface area from the optic's highly reflective, and most meaningful portion of the, parabola has been removed) and heat management (because more heat is allowed to travel into the ballast assembly through the larger diameter hole instead of being reflected towards the lens and ultimately the outside atmosphere).
Heat management suffers in the traditional design as well because the traditional design necessitates a complete separation of the light-producing module from the reflector module, i.e., the reflector is a completely separate component from the ballast, the HID lamp being rigidly attached to the ballast. Attaching the HID lamp to the ballast means that the HID lamp inductor/igniter coil is positioned on the same circuit board as the other ballast circuit components. Such a design results in intense heat production on the ballast circuit board which reduces efficiency and is not ideal. Furthermore, the high voltage inductor/igniter coil creates a significant EMF (electromagnetic field) and EMI (electromagnetic interference) field which can prove detrimental to the operation and reliability of other sensitive circuit board components; not to mention the increased threat of arcing caused by placing this high voltage unit next to other conductive components. A more ideal design would separate the HID lamp inductor/igniter coil from the ballast components to reduce ballast area heat production while increasing the ballast's reliability by separating high and low voltage segments.
Additional problems can arise when focal adjustment relies upon a reflector moving along threaded stock. In such a design, the reflector threads must be aligned perfectly upon the handle/ballast threads or upon whichever component the reflector threads mate. If the angle of the components is off when they are screwed together, the angle of the reflector will be off relative to the HID lamp, and therefore the light beam produced will be deficient. Such a misalignment may occur in production, either when the threads are cut or when the components are fitted together; may occur when the lamp is improperly seated askew in its socket; or may occur during normal use when a user attempts to adjust focus or when a user attempts to refit the reflector and the handle/ballast after taking them apart. Threaded components are easily misaligned and so such a design is clearly not ideal.